This invention relates to additive compositions, otherwise known as admixtures, for incorporation into hydraulic cement mixes, for example, hydraulic cement concretes, mortars, grouts, neat cement mixes, etc. More particularly, it relates to nonplastic cement or concrete mixes.
Nonplastic cement or concrete mixes usually contain a relatively low water content per unit volume, and are used for making "concrete masonry units" (CMUs) which include concrete blocks, concrete pavers (e.g., blocks, tiles, or other shapes used for sidewalks and pavement), and components for segmental retaining walls. Nonplastic cement or concrete mixes are also used in concrete pipes, roof tiles and pavers, and other concrete articles. Nonplastic mixes usually contain portland cement, aggregates, water, and optionally pozzolanic additions. Nonplastic mixes differ significantly from "plastic" mixes which are more workable due to a higher content of water and which normally set and harden under ambient conditions.
In contrast to plastic mixes, nonplastic mixes may be mechanically forced into molds (or extruders), and may be cured under the influence of steam and elevated temperatures. Nonplastic mixes tend to have little if any slump after being molded or otherwise formed, and have sufficient physical integrity to retain a shape without the aid of the mold or form. The resulting products, which can be cured outside the mold or form, are often called no slump or low slump concrete products.
One of the common problems of concrete products, particularly for nonplastic concrete masonry units (CMUs) such as concrete masonry blocks pavers, is the phenomenon known as "efflorescence." Efflorescence is a crystalline deposit, usually whitish in color, which appears on the surface of the CMUs and diminishes their aesthetic value. As water moves through a CMU, it picks up dissolving salts such as, for example, calcium hydroxide. As water reaches the surface of the CMU, it evaporates, leaving the salt deposit on the surface. The calcium hydroxide left on the surface reacts with carbon dioxide in the air to form calcium carbonate. In addition to calcium carbonate, the deposits may consist also of sulfates of sodium, potassium, or calcium, in addition to calcium carbonate. In extreme cases, this white rocklike deposit material may build up a surface layer inches thick.
In addition to the aesthetic problem caused by the migration of salts to the surface of the CMUs, the leaching of the materials from the interior of the CMU may create or widen a crack formation, thereby increasing the penetration of water through the crack.
Efflorescence can be designated as being "primary" or "secondary" depending upon the source of water. "Primary efflorescence" occurs during initial setting of the concrete, usually within the first 24 hours. In this case, the water source is internal. The water contained in the original concrete mix dissolves calcium hydroxide formed during the hydration of portland cement. This salt solution then migrates (ie. leaches) to the surface, where the water evaporates, and the calcium hydroxide is deposited on the surface, giving rise to primary efflorescence. The calcium hydroxide, as previously explained, can further react with carbon dioxide from the air to form the less soluble salt, calcium carbonate. Primary efflorescence is often visibly manifested as a relatively uniform haze on the surface.
Secondary efflorescence, on the other hand, is related to moisture movement within the CMU after the concrete is set and hardened. In this case, the water usually originates from outside of the CMU, is absorbed into the CMU, and therein dissolves residual calcium hydroxide which then leaches out and is deposited on the surface when the water evaporates. Again, the leached calcium hydroxide deposited at the surface may further react with carbon dioxide from the atmosphere to form calcium carbonate. Secondary efflorescence is often visibly manifested as uneven whitish streaks on the surface of the CMU, or as uniformly distributed "new building bloom." This often occurs after the CMUs are installed in place.
Admixtures are known for controlling efflorescence in CMUs. However, two different types of admixtures are required for controlling primary and secondary efflorescence.
For controlling primary efflorescence, formulations containing liquid fatty acid mixtures (e.g., oleic acid and linoleic acid) have been commonly used. The oily liquid admixture is introduced into the batch mix at an early stage by coating onto the sand particles prior to the introduction of any mix water, so that the oily admixture is distributed uniformly throughout the concrete batch mix.
For controlling secondary efflorescence, admixtures containing aqueous-based calcium stearate dispersion (CSD) are often added at a later stage of the batching process with the mix water. In a typical batching process, sand is first charged into the mixer, then the oil-based primary anti-efflorescence admixture is added with constant mixing to allow the oil to coat the sand. Then coarse aggregates, colorants, and cement are added, followed by water. If CSD is used, it is then introduced usually at this point during or after the addition of the mix water. CSD is an aqueous dispersion wherein fine solid particles of calcium stearate are suspended in the water uniformly. Commercially available CSD has an average particle size of about 1 to 10 microns. The uniform distribution of CSD in the mix may render the resulting CMU water repellent, as CSD particles are well distributed in the pores of the unit to interfere with the capillary movement of water.
However, the fatty acid mixture and the calcium stearate dispersion (CSD), as is well-known to those of skill in the art, are incompatible. Introducing these mutually antagonistic admixtures at different stages of the concrete batch mixing process creates the ever-present risk that one or the other of these admixtures may be non-uniformly distributed within the batch mix; this situation in turn gives rise to the possibility that the surface of the resultant CMU may be mottled by primary or secondary efflorescence.
To control primary and secondary efflorescence, two separate feed streams of the liquid fatty acid and CSD are required for adding the respective anti-efflorescent admixtures, at two different stages, and in a particular sequence. This method of addition causes inconvenience, decreases flexibility of processing, and increases manufacturing costs, since the process requires two different sets of dispensers and inventories.
In surmounting the foregoing and other disadvantages of the prior art, the present invention provides an admixture and methods for making and using the same, wherein both the fatty acid and CSD are pre-combined into a single product which is simultaneously effective for minimizing or avoiding both primary and secondary efflorescence.